No MBR partition was designated as active when within fdisk(8). This is a common mistake when setting up a multibooting environment.

Any partitioning created within disklabel(8) was not written to disk. Unless you chose the default partitioning scheme, it is simplest for newcomers to create one large disklabel partition encompassing however much space is available in the MBR partition for disklabel partition "a".

If you have not thoroughly read Section 4 of the FAQ, now is a good time to study it carefully.